Modern crop production systems require a high degree of precision in crop establishment and seed quality is an important factor therein. Seed quality is a complex trait that is determined by interactions between multiple genetic factors and environmental conditions. Modern approaches to improve seed quality therefore combine classical genetics, plant molecular biology and a variety of seed technologies to enhance physiological quality, vigor and synchronicity to establish uniform high quality crops in the field under diverse environmental conditions.
The commercial need for optimum seed germination performance has led to the development of processes known in the art for zygotic seeds as “seed priming.” Seed priming may be a hydration treatment that allows controlled imbibition and induction of the pregerminative metabolism (“activation”), but whereby radicle emergence is prevented. The hydration treatment is stopped before desiccation tolerance is lost. The seeds can be dried back for storage, distribution and planting. Priming enhances germination speed and synchronicity of the seeds and increases seed vigor (short or no “activation” time). Furthermore a wider temperature range for germination, release of dormancy and faster emergence of uniform seedlings is achieved by seed priming. This leads to better crop stands and higher yields.
Four techniques are currently used commercially to accomplish seed priming. These are osmopriming, hydropriming, matrixpriming and pregermination. Osmopriming (osmoconditioning) is the standard priming technique. Seeds are incubated in well aerated solutions with a low water potential, and afterwards washed and dried. The low water potential of the solutions can be achieved by adding osmotiea like mannitol, polyethyleneglycol (PEG) or salts like KCl or KNO3. Hydropriming (drum priming) is achieved by continuous or successive addition of a limited amount of water to the seeds. A drum is used for this purpose and the water can also be applied by humid air. Matrixpriming (matrixconditioning) is the incubation of seeds in the presence of a solid, insoluble matrix (vermiculite, diatomaceous earth, cross-linked highly water-absorbent polymers) with a limited amount of water. This method confers a slow imbibition. Finally, the technique of pregerminated seeds is only possible with a few species. In contrast to classical priming, seeds are allowed to perform radicle protrusion. This is followed by sorting for specific stages, a treatment that reinduces dessication tolerance, and drying. The use of pregerminated seeds results in rapid and uniform seedling development upon imbibition. During the priming of seeds (bio-)chemical compounds may be added as well such as plant hormones (e.g. gibberellins, ethylene), seed dormancy breaking compounds, fungicides etc.
Several technical and logistical difficulties have been encountered with the prior art seed priming techniques. For example, osmotic solutions require continuous aeration and in general, a large volume of priming solution is required per quantity of seeds. Immersion in liquid restricts oxygen absorption and in particular relatively high concentrations of PEG in solution render them viscous and reduce oxygen solubility and diffusion rates. Moreover, priming of large quantities of seed requires large quantities of osmotic (e.g. PEG) solution and this can cause disposal problems, particularly if fungicides have been added. Reductions in percentage seedling emergence have been reported with the use of inorganic salts. Furthermore, matrixpriming has been reported to present difficulties in separating the primed seed from the matrix (e.g. vermiculite). Also reductions in storability of primed seeds as compared to untreated dry seeds has been reported. The methods for priming seed available in the art thus far have in common that they all rely on regulating the level of hydration of the seed, i.e. the water potential, for controlling the priming of the seed. An important problem common to these water-controlled methods is to stop the priming process in the right moment, which depends on the species and the seed batch.
It is an object of the present invention to address the above problems by providing methods, compositions and devices wherein not water but rather partial oxygen pressure is used to control priming of seed.